1. Field of the Invention
The present invention relates to a method for cutting a flat tube formed by folding a plate, for example.
2. Description of Related Art
Conventionally, a sawing cutting method using a metal sawing machine and a shearing cutting method using a shearing machine are well-known for cutting a flat tube. The inventors of the present invention made a flat tube (see FIG. 1) by folding a plate, and cut the flat tube in accordance with the conventional sawing cutting method or shearing cutting method. As a result, a protrusion portion (i.e., a folded end portion of the plate) 11c of the flat tube 1 is deformed in a cutting direction of a blade portion of the cutting device used to cut the tube, as shown in FIG. 6. In FIG. 6, a locus L.sub.0 is obtained by connecting each point where a blade tip of a blade portion of the cutting device is firstly introduced into the flat tube 1 in a cutting direction. In the conventional method, since the locus L.sub.0 is parallel with the cutting direction of the flat tube 1, a cutting force F of the cutting device is applied to the protrusion portions 11a-11c at each center portion corresponding to the locus L.sub.0.
In the flat tube 1, because the protrusion portion 11c in FIG. 6 is supported only at a base portion 11e thereof, the protrusion portion 11c is readily deformed in the cutting direction so that defective cutting is caused when the flat tube is cut according to the conventional method.